Hey mrajanikrishna!

i can envision two principal approaches:

If your original image have sharp areas with no antialias (wich works as a color zone border softening), then you can use a technique called color transformation to convert every pixel but the ones with the color you want to extract to your background color (or even transparent if your image format supports it) as explained here:

http://www.aspfree.com/c/a/C-Sharp/Color-Transformation-Applications-in-Csharp-GDIplus-Programming-3/

If that`s not the case, then maybe you can try working with a similarity algorythm and then tinting the image.

Hope it works for you.